I can understand his anger, but only because of who he is and what Wikipedia is.

Wikipedia attempts to have a neutral point of view (NPOV). It is extremely nuanced but it basically means being impartial, relying on the verifiable facts & sources and not giving undue weight or emphasis on fringe views. The site also has a lot of active maintainers who go in and strive for that NPOV, deleting vandalism or other acts meant to shift away from it. It's certainly not perfect but it clearly works in the main.

NPOV is a hard thing to take for someone like Musk. He says & repeats incredibly dumb things on a daily basis and is highly susceptible to misinfo. He also has a massive ego, narcissistic personality disorder and an incredibly thin skin. He doesn't like it when somebody says something he doesn't like to hear and he doesn't like it when he can't control the person saying it. I have no idea why Wikipedia is pushing his buttons but I imagine that their bio about Musk is not pretty and it riles him up no end.